Many electrical circuits require galvanic isolation between different areas of the circuit. Galvanic isolation occurs when DC current is unable to flow between these isolated portions. However, feedback signals and other information may still need to be transmitted between the isolated portions of the circuit. One example of such an electrical circuit is a power supply or a power converter. Power supplies may be included in electrical devices such as cell phones, personal digital assistants (PDA's), laptops, etc. Because power is generally delivered through a wall outlet as high-voltage AC power the power supply or power converter is required to transform the high-voltage AC power into low-voltage DC power which may then be used to power the electrical device.
One of the electronic components often included in a power supply is a transformer. During operation the transformer allows the transfer of energy between an input side (referred to as a primary side) of the power supply and an output side (referred to as the secondary side) of the power supply. The input and output sides of the power supply are typically galvanically isolated. In this example, galvanic isolation occurs when DC current is unable to flow between the input side and output side of the power supply.
In operation, a power supply may use a controller to regulate output power delivered to an electrical device, such as a computer, that may be generally referred to as a load. The controller may also be coupled to a feedback circuit that provides feedback information about the output of the power supply so that the controller may regulate the amount of power delivered to the load.
Another feature that may be included in a power supply is a remote on/off feature. A remote on/off feature allows a device on the output side of the power supply (i.e., a load that is being powered by the power supply) to send a signal to the input side of the power supply to turn off circuitry at the input side to conserve energy. For example, a personal computer receiving power at the output side of a power supply may include an on/off switch which sends a signal to the input side of the power supply for it to turn off.
However, as stated above, the input and output sides of the power supply are galvanically isolated. Thus, the feedback information from the output and the remote on/off signal are also isolated from the input side of the power supply.